Hexavalent Chromium Testing

Chromium occurs in the environment primarily in two valence states: trivalent chromium (chromium+3) and hexavalent chromium (chromium+6). Exposure may occur from natural or industrial sources of chromium. Chromium+3 is much less toxic that chromium+6. The respiratory tract is also the major target organ for chromium+3 toxicity, similar to chromium+6. Chromium+3 is an essential element in humans. The body can detoxify some amount of chromium+6 to chromium+3.

Chromium+3 occurs naturally (widely distributed in soils and plants, but is rare in natural waters) and is an essential nutrient (necessary for metabolism of sugar, protein and fat). Chromium+6 is generally associated with industrial processes, though it does occur naturally in very small amounts.

Hexavalent chromium (chromium+6) has had widespread, long-term use in industry for its ability to inhibit the formation of rust. It is also a known human carcinogen that has impacted drinking water aquifers in some states, resulting in well shutdowns. There are few federal or state regulatory standards for hexavalent chromium; however, that is changing. For now, many regulatory standards being used apply to total chromium levels -- the combined concentrations of trivalent and hexavalent chromium. In some cases, if the total chromium concentration in a sample meets or exceeds a certain level, you must test for hexavalent chromium. Contact your regulatory agency for the most current information.

ALS Environmental employs a number of different methods for the analysis of hexavalent chromium. These include procedures that utilize ion chromatography (low-level applications for aqueous samples), colorimetric chemistry, chemical separation by co-precipitation, and chelation/solvent extraction. ALS Environmental Services also provides ancillary testing used to characterize environmental systems for the purposes of predicting the fate of hexavalent and trivalent chromium. These include sulfide (total, acid soluble, dissolved, and AVS), ferrous iron, and redox potential.

Testing Hexavalent Chromium by EPA Method 218.6

An effective method for testing drinking water for hexavalent chromium is by EPA Method 218.6 using ion chromatography. EPA's current recommended goal for hexavalent chromium is 0.06 ppb and the State of Calfornia’s new proposed public health goal is 0.02 ppb.

Testing High Chemical Interference Samples by EPA Method 7199

In situations where the matrix is highly colored or those containing a number of chemical interferences, a better method to use to test for hexavalent chromium is EPA Method 7199, an ion chromatography (IC) method. In Method 7199, the chromium+6 ion is separated from other chemicals that may cause interferences and is then followed by post column reaction with diphenylcarbazide. The IC method is much more sensitive than the colorimetric procedure. The reporting limits are typically a hundred fold lower depending on the nature of the matrix being tested. In addition, the automated nature of the samples once they are prepared allows for relatively quick analysis time.